A few days ago the British newspaper The Independent had an article entitled Do you believe in ghosts? Leading psychologist claims it's 'all in the brain.' The article then discussed the views of Christopher French, head of the Anomalistic Psychology Research Unit at the University of London. French champions the theory that ghost sightings are caused by psychological issues in those who report the sighting.
French is not actually a “leading psychologist” in the sense of being well known. He is the only professor in his Anomalistic Psychology Research Unit, whose staff consists only of himself, a research assistant, and some PhD students. French founded the unit himself. Judging from the front web page of the unit's web site, this particular academic unit seems to be basically a kind of ideological arm designed to support Professor French's skeptical prejudices. The third paragraph of the unit's web page creates the strong impression that its investigators have pretty much already made up their minds before they even do their research:
and related beliefs, and ostensibly paranormal experiences in terms
of known or knowable psychological and physical factors...
Anomalistic Psychologists tend to start from the position that paranormal forces
probably don't exist and that therefore we should be looking for other kinds of
explanations, in particular the psychological explanations for those experiences
that people typically label as paranormal.
French then attempts to suggest that ghost sightings may be hallucinations, saying "we could all have them under appropriate circumstances." He seems to insinuate that ghost sightings are produced by fear. An interesting hypothesis – you go to a haunted house or graveyard, and then you get scared so bad, you start hallucinating. However, the idea is pure bunk. There is no significant evidence that fear can cause people to have visual hallucinations.
Artisitic depiction of a ghost sighting
This link discusses the reasons for hallucinations, mentioning things such as brain disease, substance withdrawal (such as an alcoholic's delirium tremens or DT's), drowsiness, poisoning, taking certain types of drugs, sensory deprivation, and so forth. There is no discussion at all of hallucinations caused by sudden fears, because there is no real evidence that such a thing can happen. This link mentions dozens of causes of visual hallucinations, but does not list fear or anxiety as a cause.
This PDF discusses dozens of causes of auditory and visual hallucinations, but does not mention fear or anxiety.
I was there in my foxhole, and the enemy started to shell us with their artillery. I could see and hear shells exploding not far away. Then suddenly I saw a ghost in my foxhole.
As I walked down the narrow dark alley at night, I saw the shape of a big hulking guy ahead of me. I was terrified that he would mug me. Then suddenly I saw a ghost in the alley.
I was driving when the road was rather icy. Suddenly my car went into a 180 degree spin. I was terrified! Then suddenly I saw a ghost in my car.
Nobody makes reports like these, because fear does not cause people to have visual hallucinations of ghosts or anything else.
Looking at it from a Darwinian standpoint of natural selection, it is easy to understand why evolution would probably never allow a situation where fear was the cause of hallucinations. Having hallucinations in a threat situation would lower the chance of an organism surviving. If you have a hallucination while faced with some threat such as an attacking animal, you are less likely to focus on the real threat and survive the situation. Organisms which had such hallucinations would be more likely to die out, less likely to pass on their genes, and more likely to become extinct.
One reason why French's explanations fall flat is that most reports of ghost encounters do not occur at a moment when people are scared (although fear often follows such claimed encounters). One common type of ghost encounter seems to be what are called “crisis apparitions,” a type where one person reports unexpectedly seeing an apparition of a recently dead person. Cases of this type were exhaustively documented in the classic work Phantasms of the Living (which can be read here). There are also sites that are involved repeatedly in ghost reports, but the “ghost encounters” at such sites seem to occur at unpredictable, random intervals, with typically years between reports. In the latter cases, the reported ghost sighting typically occurs as a sudden surprise, not as something that was preceded by fear.
Along with near-death experiences, the phenomenon of apparition sightings is an ongoing thorn in the side of materialists who rigidly cling to the idea that consciousness cannot exist outside of the brain. Conceivably one day after we unravel all the mysteries of the brain, we might have some purely psychological explanation of ghost sightings. But judging from his newspaper interview, French doesn't seem to have got to first base at such a task. If he wants to score on the matter, my first suggestion is that he start out by abandoning the blatantly ideological “we've already made up our mind” attitude glaringly shown on his academic unit's web page, and that he investigate his subject matter in an impartial, objective, unbiased manner, like a good scientist should.